1. Field of the Invention
The present invention relates to a crack and thickness detecting apparatus capable of detecting a crack in a wafer and the thickness of the wafer during griding of the wafer.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines are formed on the front side of a wafer such as a semiconductor wafer to thereby partition a plurality of regions where a plurality of circuits such as ICs and LSIs are respectively formed. After the back side of the wafer is ground by a grinding apparatus to reduce the thickness of the wafer to a predetermined thickness, the wafer is cut along the division lines by a cutting apparatus to thereby obtain a plurality of individual device chips divided from each other. These device chips are packaged and widely used in electric equipment such as mobile phones and personal computers.
The grinding apparatus includes a chuck table for holding a wafer and a grinding wheel having a plurality of abrasive members arranged annularly, wherein the abrasive members of the grinding wheel being rotated are brought into contact with the back side of the wafer held on the chuck table (see Japanese Patent Laid-open No. 2005-153090, for example). During grinding of the wafer, there is a case that an unpredictable load may be applied to the wafer due to clogging of the abrasive members, falling of a lump of abrasive grains, a change in manner of supply of a grinding water, etc., causing the generation of fine cracks that cannot be visually identified. Such fine cracks cause device failure and it is therefore preferable to find the fine cracks after ending a grinding step. As an apparatus for detecting a crack in a wafer, there has been proposed an ultrasonic probe adapted to come into contact with the wafer (see Japanese Patent Laid-open No. 2011-146568, for example).